This invention relates to a dry etching method for eliminating a second insulating layer containing carbon atoms formed on a first insulating layer containing carbon atoms by use of activated reactive gas and a semiconductor device manufacturing method using the dry etching method.
A semiconductor device is required to have a more fine pattern with an increase in the integration density thereof. Further, an attempt is made to reduce an interconnection resistance and parasitic resistance in order to enhance the response speed.
In order to enhance the fine pattern technique of the semiconductor device, it is necessary to improve the resolution of a photoresist and it is effective to reduce the thickness of the photoresist in the development of the semiconductor device. Further, an antireflection layer is formed directly under a photoresist layer and the photoresist layer is patterned.
It is required to lower the interconnection parasitic capacitance in order to enhance the operation speed of the semiconductor device and a lowering in the dielectric constant (which is called Low-k layer) of an interlayer dielectric is studied. As the interlayer dielectric having a lowered dielectric constant, an organic based layer such as CF (fluorocarbon) based Teflon, a porous and relatively fragile inorganic layer such as an inorganic silicon oxide layer and an organic silicon oxide layer containing an organic component having carbon atoms in an inorganic layer can be given. The relative dielectric constant of the conventional oxide layer is approximately 4, but the relative dielectric constant of the above insulating layers is 3 or less. If an etching process is effected to form interconnection grooves and contact holes after a photoresist is patterned on the interlayer insulating layer, it is necessary to strip the photoresist in order to prepare for a case wherein an interconnection material or the like is filled in a later step.
In the conventional photoresist stripping method, a downflow ashing process for raising the wafer temperature to a high temperature of 200° C. or more and using process gas mainly containing oxygen gas is effected. In this method, the resist stripping process is realized by reacting carbon, oxygen, hydrogen atoms and the like in the photoresist with oxygen atoms in the active gas. It is considered that a reactive product obtained at this time contains CO2, CO, H2O and the like, but in order to attain a sufficiently high stripping rate, a method for raising the temperature of the semiconductor substrate to 200° C. or more to enhance the reactivity is normally used.
However, in the conventional photoresist stripping method, if a multi-layered layer having a layer containing carbon atoms is formed as an underlying layer, the carbon atoms of the underlying layer react with oxygen atoms in the active gas and are removed. Therefore, if the underlying layer of the photoresist layer is a Teflon based organic layer (Low-k layer) of CF series, the underlying layer is etched when the photoresist is stripped and there occurs a problem that a critical dimension bias (CD bias) occurs. Further, if the underlying layer is a layer (organic silicon oxide layer) formed of an inorganic layer containing carbon atoms, a carbon atom removed layer is formed on the surface of the underlying layer and a problem that the relative dielectric constant is changed occurs. At this time, since the underlying layer from which the carbon atoms have been removed is contracted, there occurs a problem that not only the CD bias is changed but also a stress is applied, thereby causing a crack.
Further, as a gas dielectric structure, a structure having a carbon layer buried in a porous insulating layer used as the underlying layer is known. The structure is formed by sequentially effecting processes for stripping the photoresist after interconnection grooves and contact holes are formed in the carbon layer, then filling barrier metal and interconnection material therein, and effecting a CMP (Chemical Mechanical Polishing) step. However, in the conventional method, there occurs a problem that carbon atoms buried in the underlying layer are ashed at the time of stripping the photoresist, the underlying layer is partly removed and, as a result, the CD bias occurs.